System and method for conditioning a signal

ABSTRACT

A method of conditioning a signal being communicated between a system to be controlled and a controller may include monitoring an actual output signal and conditioning the actual output signal. The method also includes determining the difference between the actual output signal and the condition signal and causing the actual output signal to be filtered based on the relationship between the difference between the actual output signal and the conditioned signal.

TECHNICAL FIELD

The present disclosure relates generally to a system and method forfiltering a signal and, more particularly, to a system and method forimplementing a signal conditioner that is varied based on signalposture.

BACKGROUND

Many control systems include multiple sensors to monitor various systemparameters and thereafter communicate this system information back tothe controller. Each sensor generates an output signal, which is read bythe controller, in preparation for subsequent system control. However,it is often difficult to discern the true signal from the noise if thenoise includes a similar frequency as compared to the true signal. Oneknown solution includes utilizing a band pass filter to filter noise ata first frequency and thereafter allowing the true signal frequency,which is at a second differing frequency, to pass through the filter.

Known filtering techniques include utilizing a band pass filter tofilter out noise which may be characterized within a first frequencyband and to allow the true signal, which may be characterized within asecond and different frequency band, to pass through the filter.However, band pass filters are often not acceptable since the frequencyof noise may be similar to the frequency of the true signal when thesignal is prone to fluctuation. Moreover, since the band pass filter isa passive element its effectiveness in providing a quality signal issignificantly dependent on the range of signals being filtered.

For example, U.S. Patent Application Publication No. U.S. 2001/0020789,dated Sep. 13, 2001 to Nakashima, discloses utilizing look-up tables ormaps identifiably based on desired motor/generator torque to provide theappropriate level of signal filtration. The signal from the torquesensor is input into a response characteristic compensation section ofthe motor/generator controller, such as a first order low pass filterthat transmits or passes signals at a frequency below a given cutofffrequency, and attenuates signals with a frequency above the givencutoff frequency. Unfortunately, if the torque output signal is similarin frequency to that of the system noise, then the filter is likely tobecome less effective.

Furthermore, many output signal types for use on high performingsystems, such as torque control of an electric motor, for example,require the ability to aggressively control the motor to obtain certainperformance mandates. In response to the need to provide aggressiveresponse to the speed/torque signal of an electric motor, the electricmotor tends to experience high frequency torque oscillations, which canresult in instability and/or surging of the motor. Moreover, highfrequency oscillations may cause undesirable operational noise, reducingthe useful life of the motor, and/or adversely effecting operatorcomfort in instances where the electric motor is utilized to animate awork machine, for example.

The present invention addresses one or more of the aforementionedproblems.

SUMMARY OF THE INVENTION

In accordance with one exemplary aspect of the disclosure, a method forconditioning a signal is provided. The method may include conditioning asignal being communicated between a system to be controlled and acontroller. The method may further include monitoring an actual outputsignal, conditioning the actual output signal, determining thedifference between the actual output signal and the condition signal,and causing the actual output signal to be filtered based on therelationship between the actual output signal and the conditionedsignal.

In accordance with another exemplary aspect of the disclosure, a methodfor conditioning a signal is provided. The method may includeconditioning a signal being communicated between a system to becontrolled and a controller. The method may further include monitoringan actual output signal, conditioning the actual output signal,determining the difference between the actual output signal and thecondition signal, and applying at least one of a filter and closed loopcontrol to the actual output signal based on the relationship betweenthe actual output signal and the conditioned signal.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this disclosure, illustrate several exemplary embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention. In the drawings,

FIG. 1 is a schematic view of a power module system in accordance withan exemplary aspect of the invention;

FIG. 2 is a table showing an exemplary corner frequency chart accordancewith an exemplary aspect of the invention;

FIG. 3 is a flow chart of an exemplary operation for conditioning asignal in accordance with the invention;

FIG. 4 is a graph showing the unconditioned signal and the correspondingconditioned signal for a period of time;

FIG. 5 is a table showing an exemplary tuning scheme in accordance withan exemplary aspect of the invention; and

FIG. 6 is a flow chart of a second exemplary operation for conditioninga signal in accordance with the invention.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the invention,examples of which are illustrated in the accompanying drawings. Whereverpossible, the same reference numbers will be used throughout thedrawings to refer to the same or like parts.

Referring to FIG. 1, a work system 10 may be equipped with a powersource 12 such as an internal combustion engine, for example, and atransmission 14. The transmission 14 may have neutral, a plurality offorward gear ratios, and one or more reverse gear ratios; however, italso include a wide variety of transmission types such as a continuousvariable transmission (e.g., hydrostatic, hydro-mechanical, directelectric, electromechanical, etc.) or other transmission configurationknown by those having ordinary skill in the art of transmissiontechnology.

The transmission 14 may be a hybrid transmission which divides enginetorque between an electromechanical transmission 16 and a mechanicaltransmission 18. The transmission 14 may be used to propel a machine(not shown) via a ground-engaging element 20. The ground-engagingelement 20 may include, for example, traction wheels or tracks. Theelectromechanical transmission 16 may include a power generator 22, forexample, an electric generator, operably coupled to electric motor(s)24. The mechanical transmission 18 may include a planetary gearingmechanism 26.

The motor 24 may include an output shaft 28 operably coupled to theplanetary gearing mechanism 26, and the planetary gearing mechanism 26may be operably coupled to an input shaft 30 of the power generator 22as is understood by those of ordinary skill in the art. The planetarygearing mechanism 26 may include one or more gears (not shown), clutches(not shown), and shafts, including an output shaft 32 coupled to theground-engaging element 20. The engine 12 may include an output shaft 34operably coupled to the planetary gearing mechanism 26.

The work system 10 may include a controller 36 to implement closed loopcontrol of the system 10. The control may include proportional,proportional plus integral, or proportional plus integral anddifferential, as is customary. The controller 36 may be embodied in oneor more microprocessors. Numerous commercially available microprocessorscan be adapted to perform the functions of the controller 36. It shouldbe appreciated that the controller 36 could be readily adapted tocontrol operation of the engine 12 and the transmission 14. Thecontroller 36 may be electrically coupled with a control lever mechanism38, for example, an operator-controlled lever. The control levermechanism 38 may be movable to input to the controller 36 a desiredground speed of the machine associated with the ground-engaging element20.

The work system 10 may also include one or more sensors 40 electricallycoupled to the controller 36. The sensors 40 may directly or indirectlysense output of any of the signal sources such as, for example, themotor 24, engine speed, engine load, and/or ground speed of theground-engaging element 20. The controller 36 may be configured toprocess and/or monitor signals received from the sensors 40.

Each sensor 40 provides an output signal to the controller 36 which, inturn, adapts for differing performance characteristics of the sensor 40.Generally, a band-pass filter may be employed to improve the outputsignal received by the controller, however this may be ineffective ifthe noise to be filtered is similar in stature relative to the truesignal.

Referring to FIG. 2, a corner frequency chart 42, which is specific tothe system being monitored and controlled, is provided and isrepresentative of one of the signal outputs such as engine speed, forexample. The corner frequency chart 42 includes a corner frequency axis44 and a variance axis 46. The variance may be defined as the differencebetween the true sensed signal and the filtered signal. A first region48, located along and adjacent to the corner frequency axis 44, isrepresentative of signals primarily made up of noise. A second region50, which extends along the length of the corner frequency axis 44, isindicative of signals which are largely mixed (i.e., mix between trueand noise) and cannot readily be defined. Finally, a third region 52 isprovided outside of both the first and second regions 48 and 50 and isindicative of a true signal being output by the sensor 40.

In an exemplary embodiment, a corner frequency or tuning function 54 maybe provided as an estimation to determine whether a signal is noise. Thecorner frequency function 54 includes a first slope 56, having little orno corner frequency value and is predominately used to heavily filterout noise (enclosed within the first region 48). A second and a thirdslope 58, 60 of the function 54 are respectively enclosed by the secondregion 50 (mixed noise and true signal) and third regions 52 (truesignal). A fourth slope 62 of the corner frequency function 54 is fullyenclosed by the outermost region 52 and is predominately a true signaland thus the corner frequency of the low pass filter is set high so asto not filter any of the true signal and thus the corner frequency ofthe low pass filter is set high so as to not filter any of the truesignal.

Referring to FIG. 3, an exemplary operation 100 of the work system 10 isdescribed. The operation 100 commences at step 105 and proceeds to step110 where the controller 36 receives an actual output signal indicativeof a system signal such as electric motor speed, for example, forcontrol of ground speed of the ground engaging element 20, that is, ifthe work system 10 were employed on a mobile machine for instance.Alternatively, the controller 36 may receive a actual output signalindicative of speed of the power source 12. It is envisioned that theexemplary operation 100 may be used singularly or in multiple instancesin accordance with any closed loop control system having an actualoutput signal, such signal being known to those having ordinary skill inthe art of control system technology.

Control then continues to step 115, where the filter is applied to thesignal. Thereafter in step 120, the controller 36 determines thedifference between the actual and the filtered signals. The cornerfrequency table 42 (FIG. 2) now may be utilized since the signalfrequency and the difference between the filtered and actual frequencies(variance) is known.

Next, in step 125, the controller 36 determines whether the variancebetween the actual signal and the filtered signal is small. If, in step125, the controller 36 determines that the variance is small, controlcontinues to step 130. Otherwise, if the variance is not small thencontrol jumps to step 135.

In step 140, the controller 36 establishes a conditioned signal based onthe status of the actual signal relative to the corner frequencyfunction 42. That is, if the variance is negligible the signal isconditioned by significant application of the filter. In contrast, ifthe variance, for a particular corner frequency, results in the signalhaving an unknown characteristic, then the signal is filtered, albeit toa lesser degree than if it were noise. However, as the corner frequencyof the signal increases, and additionally, the variance increases, sucha signal is more clearly classifiable as a true signal and consequentlythe filter is not employed.

As the control proceeds, in step 140, the controller 36 progresses thecontrol back to step 110 wherein a new actual signal may be determinedand a new variance calculated in preparation for continued signalconditioning.

Referring to FIG. 4, it may be seen that the true signal closely relatesto the conditioned signal when operation 100 is being employed tocontrol the speed of an engine, for example. Trace 64 includes a truespeed signal 66 and a conditioned speed signal 68. A first region 70(approximately 2110 RPM), which is indicative of noise control (heavyfilter or low corner frequency), is provided between zero and 1.5seconds. A second region 72 is indicative of a response or true signalcontrol (lighter or no filtering or high corner frequency) and isprovided between 1.5 and 6 seconds.

In addition to employing a filter which varies based on previous signalposture, it is envisioned that any closed loop control known to thosehaving ordinary skill in the art may be employed in combination with thepresent system. However, one exemplary control scheme may includeestablishing a deadband around the command for aggressively tuning thesystem when a true signal is detected.

Referring to FIG. 6, operation 200 utilizing closed loop PID deadbandcontrol will be described. The system 10 includes the controller 36 toimplement closed loop control of the system 10. The control may beproportional, proportional plus integral, or proportional plus integraland differential. The controller 36 may be embodied in one or moremicroprocessors. Numerous commercially available microprocessors can beadapted to perform the functions of the controller 36. It should beappreciated that the controller 36 could be readily adapted to controloperation of the engine 12 and the transmission 14 or other systemutilizing an output signal for the basis of control.

An exemplary operation 200 of the work system 10 commences at step 205and proceeds to step 210 where the controller 36 receives desired inputcommand, indicating a desired output of the motor 24, for example, toproduce a steady-state ground speed of the ground engaging element 20.

Control then continues to step 215, where the controller 36 determinesthe control error or the difference between the desired input commandand the monitored output of the motor 24.

Next, in step 220, the controller 36 determines whether the desiredoutput of the motor 24 is associated with a zero ground speed of theground engaging element 20. If, in step 220, the controller 36determines that the desired output of the motor 24 is not associatedwith a zero ground speed of the ground engaging element 20, controlcontinues to step 225. Otherwise, if the desired output of the motor 24is associated with a zero ground speed of the ground engaging element20, control jumps to step 230.

In step 225, the controller 36 establishes a deadband around the erroror the difference between the desired input command and the monitoredoutput. The magnitude of the deadband may be empirically determined fromthe system noise and/or poor resolution of the controller 36 and/orsensors 40.

In step 230, the controller does not apply a deadband around the erroror the difference between the desired input command and the monitoredoutput. This deadband is eliminated as precise control may be neededwhen the operator is expecting or requesting zero ground speed.

As the control proceeds, in step 235, the controller 36 determines atorque command (from adjusted difference or adjusted control error) orother suitable exemplary command and sends this torque command to step240 for operating the motor 24 to generate the desired motor output, forexample, to attain the desired steady-state ground speed.

Exemplary operation of the work system 10 utilizing the closed loop PIDdeadband control commences as an operator moves the control levermechanism 38 to command a desired ground speed of the ground-engagingelement 20. The controller 36 determines a desired output of the motor24 required to generate the desired ground speed. When accelerating ordecelerating, the controller 36 varies the torque command for operatingthe motor 24 based on the monitored output of the motor in a feedbackcontrol system, for example, a closed loop control system.

Once the ground-engaging element 20 has reached the desired speed, itmay no longer be desirable for the controller 36 to continuously varythe torque command based on minimal differences between the desiredoutput of the motor 24 and the monitored output of the motor 24.Instead, it may be more desirable to filter out the minimal differencesthat may likely be attributable to poor resolution of or noise in thesystem 10, including the controller 36, and/or the sensors 40.

The controller 36 may be operating under predominately or exclusivelyproportional control when, for example, the motor 24 is an electricmotor. In many industrial applications, the overall gain (orproportional gain) of the controller may be required to be high due tothe response requirements of the machine. Therefore, a small controlerror possibly attributable to poor resolution or noise may cause thecontroller 36 to continuously vary the torque command to attempt toattain the desired steady-state output. As a result, the motor outputmay over-respond and continuously oscillate around the desired steadystate output. In addition, it is possible, depending on the operationalfrequency of the controller 36 and the necessary frequency responsedetermined by the controller, the system 10 may over-respond and becomeunstable. By establishing a deadband around the torque command forattaining the desired steady state output of the motor, the controller36 is forced not to respond to small control errors possiblyattributable to the poor resolution or noise.

Furthermore, the controller 36 may be configured to remove the deadbandwhere small control errors should be considered. For example, when anoperator commands negligible ground speed of the ground-engaging element20, the controller 36 determines an appropriate motor output. Since itis not desirable for the ground-engaging element 20 and an associatedmachine to creep, zero steady state error is required. Therefore, whenthe desired output of the motor is associated with zero ground speed ofthe ground-engaging element 20, the controller 36 does not implement thedeadband. As a result, the controller 36 may continuously vary thetorque command for operating the motor 24 to attain the desired motoroutput.

The operation 200 of the work system 10, such as that employed tocontrol the electric motor, for example, may reduce instability and/orsurging of the work machine possibly associated with poor resolution ofand/or noise in the system 10. Further, undesirable operational noisemay be significantly reduced and, as a result, the useful life of themotor may be extended in addition to providing improved operatorcomfort. Creep of the ground-engaging element 20 may also bebeneficially reduced since substantially zero steady state error may beobtained when zero ground speed is commanded.

Referring to FIG. 5, it may be seen that a blend of filtration, pursuantto operation 100, and PID deadband control, pursuant to operation 200,may be established based on response control requirements and on theability to differentiate between noise and the true signal (value of thevariance parameter). For instance, if there is little response requiredand the noise can be differentiated from the true signal (variancebetween the signal and the filtered value is negligible), then the fulloutput of the filter is applied. Conversely, if the noise cannot bedifferentiated well (variance between the signal and the filtered valueis significant) and a fast or high response control requirement iswarranted, then the filter is negated (or significantly reduced) andfull PID control with deadband is employed. When the contribution effortcomprises a blend of PID control with deadband and filtrationeffectiveness for a particular response requirement, then exemplarycontribution efforts may be provided as seen in FIG. 5.

INDUSTRIAL APPLICABILITY

In operation of work system 10 (FIG. 1), pursuant to operation 100 (FIG.3), as the operator moves the control lever mechanism 38 to command adesired output for the work system 10, such as the speed of the powersource 12, and/or the speed of the ground engaging element 20, theoutput signal is developed and depending on its condition or posture,the filter will be applied.

The operation which conditions the output signal using substantially allof the filter and falls within the first region 48 (FIG. 2) of thecorner frequency chart 42 will now be described. Since the noiseassociated with such operation typically has a given variance band ofapproximately 10 to 15 RPM during steady-state conditions, thecontroller deems the variance to be characterized as “small” (box 125 ofFIG. 3). Then, the signal is heavily filtered with a corner frequencyrelatively small (the relatively small nature of the corner frequency issystem dependent but typically will be less than 0.5 Hz, for example).

The operation which conditions using substantially none of the filter,such signal type falling within the third region 52 of the cornerfrequency chart 42, will now be described. When the output signal haschanged such that it is larger that the typical noise or variance, thenthe speed signal is considered to be substantially true. Consequently,when the variance is determined to be significant, the speed signal isthereafter lightly filtered with a corner frequency relatively high(depending on the specific system or machine application which may be 7to 8 Hz, for example).

Operation which is clearly neither noise nor a true signal falls withinthe second region 50 of the corner frequency chart 42 and includes thestatus of unknown (signal being a mixture of both noise and a truesignal). When the output signal is changed such that its variance islarger that the typical noise, then the speed signal is considered to beunknown and an intermediate amount of filtration may be applied tocondition such signal. Alternatively, the unknown signal may be leftunfiltered as a conditioning alternative and the subsequent signal maybe subsequently interrogated to determine its disposition so that asuitable signal conditioning may be later applied. The first, second,third and fourth slopes 55, 58, 60 and 62 of the corner frequencyfunction 54 may be stored within the controller as dividing lines fordetermination of a signal's status or posture.

Contribution of Filter and Closed Loop PID Deadband Control

Referring to FIG. 5, the work system 10 (FIG. 1) may be operatedpursuant to a blended combination of operation 100 (filter) andoperation 200 (PID control) to, inter alia, produce the desired controlsystem over a wide operating range of the system 10. Notably, the tuningrequirement may be defined as the amount that each individual algorithm(100 and 200) will contribute to eliminating the system fromover-responding to the false or noisy feedback signals while allowingthe system to respond to the true signals.

When substantially all of the contribution effort is provided by theclosed loop PID deadband control 200, the PID deadband control 200 issubstantially responsible for eliminating over-responsive signals, falsesignals and noisy feedback. Notably, a substantially true signal hasbeen detected and the system response and performance is most effectivewith PID control without interference from band filtering.

Conversely, when substantially all of the contribution effort isprovided by the filter, the filter control 100 is substantiallyresponsible for eliminating over responsive signals, false signals andnoisy feedback. Notably, a substantially steady-state signal has beendetected and, accordingly, signal conditioning to provide high responseis not warranted. Rather, to prevent over-response of the signal, thefilter may be employed to prevent false and undue system responses.

It may be seen that the contribution of filter and PID control withdeadband may be blended to obtain a performance conditioning based onthe response control requirement and the ability to differentiatebetween noise and the true signal. For instance, if a high or fastresponse were warranted then the significant contributor would be thePID control with deadband. However, if medium response control wererequired and the ability to differentiate the signal were poor then afilter range between 5-35% combined with a PID control with deadbandrange between 65-95% would be effective. Notably, as the ability todifferentiate the noise from the true signal increases the contributioneffort of the filter is increased (for example 50% filter, 50% PIDcontrol with deadband for medium response control). Further, if slowresponse control is a requirement and the ability to differentiate thesignal is poor then a filter range between 50-70% combined with a PIDcontrol with deadband range between 30-50% would be effective. Notably,as the ability to differentiate the signal increases the contributioneffort of the filter is increased (for example, as high as 95% filterand 5% PID control with deadband for slow response control).

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the disclosed system andmethod for conditioning a signal without departing from the scope orspirit of the invention. Other embodiments of the invention will beapparent to those skilled in the art from consideration of thespecification and practice of the invention disclosed herein. It isintended that the specification and examples be considered as exemplaryonly.

1. A method of conditioning a signal being communicated between a systemto be controlled and a controller, the method comprising: monitoring anactual output signal; conditioning the actual output signal; determiningthe difference between the actual output signal and the conditionedsignal; and causing the actual output signal to be filtered based on therelationship between the actual output signal and the conditionedsignal.
 2. The method according to claim 1 wherein conditioning theactual output signal includes one of applying a filter to the actualoutput signal or refraining from applying a filter to the actual outputsignal.
 3. The method according to claim 1 wherein filtration of theactual output signal is based on predetermined corner frequency dataassociated with the actual output signal.
 4. A method of conditioning asignal being communicated between a system to be controlled and acontroller, the method comprising: monitoring an actual output signal;conditioning the actual output signal; determining the differencebetween the actual output signal and the conditioned signal; andapplying at least one of a filter and closed loop control to the actualoutput signal based on the relationship between the actual output signaland the conditioned signal.
 5. The method according to claim 4 furthercomprising applying at least one of a filter and closed loop control tothe actual output signal based on a response control requirement.
 6. Themethod according to claim 4 wherein the closed loop control consists ofPID closed loop control with deadband.
 7. The method according to claim4 wherein the closed loop control includes determining a differencebetween the actual output signal and a desired input command signal,establishing a deadband around the difference and applying the closedloop control to the actual output signal based on a relationship betweenthe difference and the deadband.
 8. A method of controlling a motor, themethod comprising: monitoring an actual output signal of the motor;conditioning the actual output signal of the motor; determining thedifference between the actual output signal and the conditioned signal;and causing the actual output signal to be filtered based on therelationship between the actual output signal and the conditionedsignal.
 9. The method according to claim 8 further comprising applyingat least one of the filter and closed loop control to the actual outputsignal based on the relationship between the actual output signal andthe conditioned signal.